1. Field of the Art
The present invention relates to a pipe connection structure and a vacuum-type sewage collecting apparatus incorporating the pipe connection structure.
2. Prior Art
Hitherto, a vacuum-type sewage collecting apparatus has been known as an apparatus for collecting sewage from a plurality of houses or facilities.
FIG. 4 illustrates the overall structure of a conventional vacuum-type sewage collecting apparatus of the type described above.
As shown in the drawing, sewage discharged from each of houses 30 on the ground passes under natural flow through sewage pipes 31 disposed underground until it flows into cesspools 32 disposed more deeply underground. When a predetermined quantity of the sewage accumulates in an underground cesspool 32, a vacuum valve 33 provided in the upper portion of the inside of the cesspool 32 is opened so that sewage accumulated in the cesspool 32 is sucked through a suction pipe 34.
The sewage sucked through the vacuum valve 33 via suction pipe 34 is introduced into a vacuum sewage pipe 1 arranged underground. Then, it is accumulated in an accumulating tank 41 in a vacuum pump plant 40.
The sewage accumulated in the accumulating tank 41 is then sent to a sewage treatment plant or the like by a feeding pump 42. A vacuum pump 43 is connected to the accumulating tank 41 to create negative pressure in the accumulating tank 41 and the vacuum sewage pipe 1.
FIG. 5 is a schematic view which illustrates a network of vacuum sewage pipes 1 for use in a vacuum-type sewage accumulating apparatus of the type described above.
As shown in the drawing, one or a plurality of main pipes 1-1 are connected to the accumulating tank 41. Furthermore, a plurality of branch pipes 1-2 are connected to the main pipe 1-1. In addition, lateral pipes 1-3, to which the vacuum valves 33 are connected, are connected to the main pipes 1-1 or the branch pipes 1-2. The pipes are thus branched from one another underground.
FIG. 6 is a side elevational view which illustrates the shape of the main pipe 1-1 or branch pipes 1-2 constituting the vacuum sewage pipe 1 embedded underground.
As shown in the drawing, the main pipe 1-1 or the branch pipe 1-2 includes downward-slope portions 11 which extend downwardly towards the accumulating rank 41 in the vacuum pump plant 40 and a lift portion 12 fastened to the lowermost portion of a downward-slope portion 11. The lift portion 12 has a steep upward slope of about 45.degree.. These downward-slope portions 11 and the lift portions 12 are provided alternately so as to exhibit a sawtooth-shaped configuration.
The reason for the provision of the lift portion 12 lies in that if the vacuum sewage pipe is constituted only by the downward-slope portions 11, the underground depth of the pipes becomes too deep.
The sewage, which has passed through the downward-slope portion 11, clears the lift portion 12 by the effect of the negative pressure supplied from the accumulating tank 41 and again passes through the next downward-slope portion 11. As a result, the sewage flows to the accumulating tank 41.
FIG. 7 illustrates a conventional structure for establishing a connection between the main pipe 1-1 and the branch pipe 1-2.
As shown in the drawing, hitherto, the branch pipe 1-2 has been connected to just the upper portion of the main pipe 1-1.
If the branch pipe 1-2 is fastened to just the side of the main pipe 1-1 as shown in FIG. 8, an opening 16 at which the branch pipe 1-2 communicates with the main pipe 1-2 may become clogged with sewage. This leads to a fact that air a in the main pipe 1-1 and air b in the branch pipe 1-2 are separated from each other, causing a backward flow of the sewage in the main pipe 1-1 toward the branch pipe 1-2 if the pressure of air b becomes lower than that of air a. Therefore, the branch pipe 1-2 is instead fastened to the upper portion of the main pipe 1-1 as shown in FIG. 7.
Since the above-described problem would otherwise occur in the junction between the main pipe 1-1 and the branch pipe 1-2, the junction between the main pipe 1-1 and the lateral 1-3, and the junction between the branch pipe 1-2 and the lateral 1-3, a similar connection structure is employed for each of the above-described branched portions.
However, in the case where the branch pipe is connected to the upper portion of the main pipe, the following problems arise.
(1) Problem in Terms of Strength
As shown in FIG. 7, if the branch pipe 1-2 is fastened to the upper portion of the main pipe 1-1, the distance m between the bottom of the main pipe 1-1 and the bottom of the branch pipe 1-2 is excessively large. Therefore, when the thus connected main pipe 1-1 and the branch pipes 1-2 are laid underground, the level n of portion g of the branch pipe 1-2 adjacent to the junction thereof with the main pipe 1-1 is considerably high from the bottom of a groove 35, which was excavated to the depth l to accommodate the main pipe 1-1.
As a result, the branch pipe 1-2 is laid on soft and thick earth placed to recover the groove 35. However, the recovering earth is too soft to support the branch pipe 2 at its lower side. Therefore, when the load from ground level and the weight of the recovering earth above the branch pipe 1-2 are applied thereto, the portion g of the pipe 1-2 receives an excessive load. As a result, a problem arises in that the branch pipe 1-2 may be easily broken. The above-described problem becomes critical in the case where the vacuum sewage pipe is embedded under the ground on which vehicles or the like run.
(2) Problem in Terms of the Depth of the Pipe
In general, when a vacuum sewage pipe is laid underground, it must be placed at a certain depth in order to disperse the load from ground level applied to the vacuum sewage pipe. Furthermore, in cold areas, it must be laid at a considerable depth so as to prevent it from freezing.
However, as shown in FIG. 7, if the branch pipe 1-2 is fastened to just the upper portion of the main pipe 1-1, the position of the branch pipe 1-2 becomes considerably high relative to the main pipe 1-2. Therefore, in order to lay the branch pipe 1-2 at a predetermined depth, the main pipe 1-1 must be laid at a greater depth. As a result, the excavating work is difficult, resulting in an undesirable raising of costs.